Improvement in tanning



' Umireo STATES PATENT ()FFICE.

CHARLES L. ROBINSON, OF WAUKESHA, ASSIGNOR T0 HIMSELF AND THOMAS G.EGGLESTONE, OF FOX LAKE, WISCONSIN.

IMPROVEMENT IN TANNING.

Specification forming part of Letters Patent No. 27,259, dated February21, 1860.

To all whom it may concern:

Be it known that I, CHARLES L. ROBINSON, of Waukesha, in the county ofW'aukesha and State of Wisconsin, have invented a new and usefulImprovement in Tanning Skins and Hides of all Descriptions; and I dohereby declare that the following is a full, clear, and exactdescription of the same.

Myinvention consists in the employment, in combination with a liquor ofterra-japonica which has been purified with sulphuric acid, ofcarbonate, sulphate, or calcined magnesia and sulphate of potassa, asand for the purposes hereinafter specified.

To enable others skilled in the arts to make and use my invention, Iwill describe it as clearly and briefly as possible.

I first make up my terra-japonica tanningliquor, which I call No. 1, asfollows: I put about one hundred and twelve (112) gallons of water intoa suitable kettle heated over a fire, and add fifteen (15) pounds ofcommon terrajaponica to it, and while the heat in the fire is continuedI stir up the liquor until it (the terra-japonica) is dissolved. I alsoadd to this three (3) ounces of common sulphuric acid very cautiously,and stir the liquor rapidly. It is dangerous to pour in strong sulphuricacid into hot water. Thereforeitshould either be poured in when thewateris cold, or otherwiseit should be greatly diluted. This combineswith impurities in the catechu and precipitates them. I now bringthisliquor to the boiling-point and skim ofi' all the froth which risesto the surface. I then pour out this liquor into a large tank or woodenvessel to cool. During this period of cooling a considerable amount ofsediment falls to the bottom. This consist of insoluble impurities whichnot only retard the tanning process, but injure the quality of theleather if retained in the tanning-vats. These impurities consist oflime, albumen, gummy and resinous matter, and sometimes starch, which isemployed for the purpose of adulteration, and they frequently amount tofrom thirty to forty per cent. of the solid parts of the terra-japonica.The lime and the resin tend to render the color of leather very dark,and they also make it very brittle. In precipitating them withsulphnricaeid I use such a quantity of the latter as will not sensiblyaffect the i tannin, while it removes the injurious substances. I nowrack 0d the clear liquor from the cooling-tank into a vat, (leaving thesediment behind,) and use it as follows For upper-lztthen-J add to thequantity of racked-off liquor No. 1 described about onefourth of anounce of dissolved carbonate or calcined magnesia and about thesixteenth of an ounce of sulphate of potassa, and. thenadd as much wateras will reduce liquor No. 1 to one-half its strength, which will beabout a sufficient quantity for ten good-sized hides. The whole is nowstirred up and forms the tanningliquor No. 2. The hides are now enteredin this liquor and are moved frequently the first two days, so as toallow the substances in the liquor to act uniformly and at the same timeprevent the hides becoming spotted on those places where they come incontact with one another.

Fresh clear liquor No.1 must always be kept prepared and at hand to keepup and increase the strength of the vat-liquor No. 2, in which the hidesare being tanned. About thirty-five gallons ofit are added every secondday at the early stage of the process, and one ounce of sulphate ofmagnesia. The hides are lifted out to putin the freshliquor. I willstate here that the quantity of magnesia sulphate added will depend uponthe amount of plumping which the hides require. The practical tannerwill judge of this by inspection. Great-er quantities of fresh liquorare added toward the end of the process, so as to increase the strengthof liquor No. 2. The same practice is pursued in this respect as intanning with oak and hemlock liquors. When the hides are perfectlytanned they are lifted out of the liquor and atterward treated exactlylike hides tanned by common processes. It requires from two to fourweeks to tan cowhides for upper leather, as described, and when theoperation is effected perfectly the tanner can judge by examining thehides.

This method of tanning is suitable for all upper-leather, for calf,sheep, and other skins, with the hair removed, or with the fur retained.Furs tanned in this manner are free from the attacks of moths andinsects. In tanning calf, goat, sheep, and other skins and furs it ispreferable to employ a liquor somewhat weaker than No. 2; but otherwisethe process is ex actly the same. The length of time for effectingcomplete tannin g of any skin depends much on its size and thickness;but it is only by the usual method of inspection that a tanner can judgewhen the skin is completely tanned. About one hundred skins or fiftycalf-skins may be tanned in the same quantity of liquor as that for theten hides already described.

Harness and sole leather.Such leather is made harder and more firm thanupper-leather; but the liquor for cow and ox hides to make it is made upexactly like No. 2 described, and the process conducted in the samemanner, with the exception that two ounces of sulphate of potassa areemployed or added to the first liquor which the hide receives. This saltrenders the sole-leatherhard and firm. If a large quantity were used forupper-leather, it would make it too hard. In tanningsole-leather thesame method of operating is pursued as for upper-leather, the liquorsbeing made stronger toward the end of the process. It takes from four toeight weeks to tan harness-leather, and from six weeks to three monthsto tan soleleather by my improved liquors. Furs and sheep-skins may betanned in from ten to fourteen days. The sulphuric acid acts the part ofan alterant, as well as a purifier of the catechu, as the colorsproduced in the hides and skins tanned by my process are a beautifuldark cream.

My improvement does not quicken the process of tanning materially fromthe old method,

although it is somewhat quicker, butit makes far superior leather tothat which has hitherto been produced. By removing the resin, the

lime, and other impurities from terra-japonica, as described, theleather which I produce is free from all brittleness, is more flexible,stronger, and durable than common barktanned or other catechu-tannedleather.

So far as I am able to judge the magnesian salts seem to have the effectof keeping the pores of the skins open to permit the tannin to enter andcombine with the gelatine in the interior of the skin. The potassa saltappears to possess the quality of compacting the fiber and rendering theleather firm.

In making up new vats old liquors are used in place of water when thesecan be obtained. In tanning with terra-japonica the operations are morecleanly, simple, and less laborious than in tanning with bark, andbesides the business may be conducted, whenever water can be obtained,altogether independent of our hemlock and oak forests, which are rapidlydisappearing.

I am aware that sulphuric acid has been used in tanning, but not in themanner nor for the same purpose as it is used by me.

VVhatIclaim as myinvention, and desire to secure by Letters Patent, is-

The employment, as and for the purpose herein specified, in combinationwith the purified terra-japonica liquor herein described, of carbonate,sulphate, or calcined magnesia and sulphate of potassa iii-about theproportions herein set forth.

OHS. L. ROBINSON.

Witnesses:

W. TUsoH, R. BoEKLEN.

